Termite damaged wood in an old house

Dear Home Inspector: We are buying a 200-year-old stone farmhouse.Extensive termite damage and rot in the joists was discovered. We havebeen told we should replace the joists rather than treat them and sister newjoists on. Which is better to ensure no future infestation? We are new to thehistoric home owning and not sure what is best."

Termite "shelter tube" on a wood joist Photo: Wm. Kibbell

The best course of action to prevent future infestation, after treatment, isto eliminate any conditions conducive to wood destroying insects.

Stonebuildings typically have the floor joists inserted into pockets of thefoundation wall. Moisture wicks into the ends of the joists, creating rot andattracting insects.

Also, elevated humidity levels throughout the basement orcrawlspace keeps the moisture percentage at a level that can sustain activity ofseveral types of wood destroying insects.

Proper positive slope grading around the perimeter of the home cansignificantly reduce moisture levels on the interior. Just as important is aneffective gutter and downspout system to collect and discharge roof run-off awayfrom the foundations. Also, if you use a sump pump, be sure it discharges wellaway from the foundation. Often times, open window wells or basement stairwellstrap water against the foundation. Any exposed soil inside a basement orcrawlspace should be covered with at least a plastic vapor barrier.

If the infestation is from subterranean termites, be sure to eliminate anywood that is in direct contact with soil. On the exterior of a stone house, thebasement window frames are the most common entry point for termites. On theinterior, support posts or stairs may be in direct contact with soil.

An experienced and conscientious exterminator that treats for termites shouldalso form an overall plan of action beyond just injecting chemicals. Any"shelter tubes" should be cleaned off and all termiteinfestation/damage should be documented in a detailed diagram so that futureinspections will reveal any re-infestation or new damage. A renewable andtransferable warranty should also be provided and it should include annualinspections.

A majority of the termite damage I have seen to floor structures usually onlyneeds reinforcement. This typically involves sistering joists and adding beamswith columns where the joists attach to the exterior foundation walls. Usingpressure treated wood for these repairs would be my preference.

About the AuthorWilliam Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.